Abstract
The daytime plasma density disturbances in the low-latitude ionosphere, referred to as plasma irregularities, mainly occur during the nighttime and are an unusual phenomenon. Based on the observations from multiple low Earth orbiting (LEO) satellites, e.g., the Defense Meteorological Satellite Program (DMSP) F13 and F15, the first Satellite of the Republic of China (ROCSAT-1), the Gravity Recovery and the Climate Experiment (GRACE), and Challenging Mini-satellite Payload (CHAMP) satellites, as well as the ground-based Global Positioning System (GPS) receivers, we report a special event of low-latitude plasma irregularities that were observed after sunrise in the Pacific longitudes on 18 August, 2003, following a moderate geomagnetic storm. Observations from three ground-based GPS stations in both hemispheres showed remarkable total electron content (TEC) disturbances during 20:00 to 21:00 UT (around local sunrise), agreeing well with the in situ plasma density irregularities recorded by the nearby flying LEO satellites. The plasma irregularities observed by these LEO satellites showed quite different depletion intensities at different altitudes. We suggest that the plasma irregularities were freshly generated near sunrise hours due to the disturbance of the dynamo electric field (DDEF), evolving into the post-sunrise and morning sector, but were not the remnant of the plasma irregularities generated during the previous nighttime.
Highlights
After sunset, the vertical density gradient becomes steep at the bottom-side of the equatorial F-layer due to the rapid uplift of the F-layer, and the Rayleigh-Taylor (R-T) instability is triggered to generate plasma density irregularities, which are usually referred as Equatorial Spread F (ESF) or plasma bubbles, manifesting as plasma density depletions [1]
Tulasi Ram et al [10] displayed the occurrence of fresh field-aligned irregularities (FAIs) near the sunrise terminator during a minor geomagnetic storm, and the FAIs persisted into the post sunrise periods for more than 90 min, which was attributed to the prompt penetration of overshielding electric fields
The occurrences of the daytime irregularities, in this case, can be concluded as: (1) at first, the R-T instability was triggered near sunrise at the bottom of the F-layer due to the disturbance of the dynamo electric field (DDEF), and plasma irregularities generated; (2) plasma irregularities evolved into two hemispheres, with the poleward motions; (3) the density depletions became larger under the effects of the polarization eastward electric field, and moved upward, lasting for more than 3 h into local morning sector, which were detected by ground-based global positioning system (GPS) observations and Challenging Mini-satellite Payload (CHAMP), Gravity Recovery and the Climate Experiment (GRACE), ROCSAT-1, Defense Meteorological Satellite Program (DMSP) F15 satellites in both hemispheres successively, and the depletion magnitude reached the maximum at CHAMP altitude, with a magnitude of about 70%
Summary
The vertical density gradient becomes steep at the bottom-side of the equatorial F-layer due to the rapid uplift of the F-layer, and the Rayleigh-Taylor (R-T) instability is triggered to generate plasma density irregularities, which are usually referred as Equatorial Spread F (ESF) or plasma bubbles, manifesting as plasma density depletions [1]. Sripathi et al [12] reported the presunrise occurrences of plasma bubbles in the Indian sector during a moderate geomagnetic storm, and they indicated the penetration electric field and disturbance dynamo electric field can trigger the development of the bubbles locally. Park et al [15] reported a dayside plasma depletion at midlatitude region (magnetic latitudes: 25◦~30◦) by the Swarm and Gravity Recovery and Climate Experiment (GRACE) satellites, during quiet geomagnetic condition, which later has been confirmed to be caused by the rocket exhaust [16]. We present a case study of daytime plasma irregularities in both hemispheres after sunrise, around the 160◦E region, recorded by Defense Meteorological Satellite Program (DMSP) F13 and F15 satellites during the recovery phase of a storm. Remote Sens. 2020, 12, 2897 hemisphere are presented, respectively, to investigate the performances of the plasma irregularities and possible mechanism leading to the occurrence of the daytime plasma irregularities
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